Since the invention of the atomic force microscope (AFM), it has been proven to be a very powerful tool for characterizing surface features from the micrometer scale to the atomic scale. Beside its capability as a measurement instrument, the AFM has also been exploited in recent years to modify the sample surface through nanomaniplation by many research groups. Some of them are trying to utilize the haptic devices to facilitate the nanomanipulation. Unfortunately, the implementation of the haptic nanomanipulation is hindered by the difficulty to obtain reliable force information because of the softness of the conventional cantilever.
Because the conventional cantilever is very soft, a preload normal force has to be applied on the tip in general case in order to keep the tip contacting the surface and overcome the tip slipping over the nano-object. The preload normal force is usually much stronger than the tip-object interaction forces, which make the haptic feeling dominated by the preload force. Therefore, it becomes difficult to feel the actual tip-object interaction force during manipulation. It also becomes very difficult to precisely control the tip position in the lateral direction during manipulation because the preload force causes the cantilever not only to bend in the normal direction but also cause the tip to move in the lateral direction. Consequently, the nano-object may easily be lost during nanomanipulation. Furthermore, the preload force will wear out the tip and cause contamination easily. Therefore, a rigid cantilever is preferred for AFM based nanomanipulation. However, since the interaction force is measured from the deflection of the cantilever and a rigid cantilever won't be deflected by the interaction force, the interaction force is undetectable with a rigid cantilever. Hence, it is a dilemma whether to use a soft cantilever or a rigid one for nanomanipulation. Thus, any technique that possesses the advantages of soft cantilever and rigid cantilever simultaneously will help to perform AFM based nanomanipulation without the preload force on the cantilever-tip.
Therefore, it is desirable to provide an active probe for use as an end effector for an AFM-based nanomanipulation system. During imaging mode, the active probe is controlled to bend in the same direction as the interaction force between the tip and samples and thus make the tip response faster, increase the imaging speed, and improve the image quality. During manipulation mode, the active probe is controlled to be rigid and maintain its straight shape, and thus the deformation of the cantilever is eliminated during manipulation. At the same time, the control signal is used to represent the interaction force. Hence, the active probe can be used to improve the accuracy of nanomanipulation and the force sensitivity of the haptic nanomanipulation system simultaneously. Since the cantilever keeps straight during manipulation and is adaptable to different sized objects, it is called adaptable end effector. A control algorithm, to keep the cantilever straight during nanomanipulation, is also proposed based on the developed model of the flexible cantilever. A preload force of the cantilever is no longer needed and the position control is significantly improved since the cantilever can maintain its straight shape during nanomanipulation.